1. Field of the Invention
This invention relates to a filter cartridge comprising, in its annular receiving space formed between a central flow passage, and its peripheral wall in which there are through-flow apertures, a filter element traversed substantially radially in respect of the receiving space by the medium which is to be filtered, the filter element being supported in a leak-proof sealed fashion between end caps which support its two ends.
2. DESCRIPTION OF THE RELATED ART
In practice, winding modules are known in which a uniform deep filter fleece or threads are wound spirally around a draining central tube. Winding modules of this type have the disadvantage that when filtering very clouded substances they become blocked very quickly. The cause of the rapid clogging of this type of rolled cartridge is the fact that they exhibit an homogeneous construction, i. e. an even retention characteristic, over their entire depth. Due to the spiral winding process, only the outer layer which is accessible to the fluid becomes involved and clogged. The layers underneath remain unaffected.
Winding modules are also known which instead of strip-like filter fleeces have threads of differing thickness which are wound on bobbin-like forms and which may for example be connected to one another by heat (U.S. Pat. No. 4,112,159). The disadvantage of these winding modules lies in the fact that they are built up from pure spun polyolefin threads (e. g. polypropylene) and consequently do not have the good particle retention for which the strip-like filter layers are well known, so that they are not suitable for filtering heavily colloidal turbidity-laden substances.
Furthermore, winding modules are known which, with a flat filter strip with a draining supporting and spacing holder are welded or glued or rolled onto one another in a coincident relationship to form closed strips (DE-PS 37 40 249). The disadvantage of winding modules of this type is that the different filter or draining strips and spacers are placed on one another in separate operations and have to be welded or glued to one another to form endless strips. Modules of this type are severely labor-intensive and render automatic and rational production difficult. Apart from the fact that the filter strips or drainage fabrics, as well as the spacers, cannot be welded in a leak-proof fashion, there is the risk of a short circuit between filtrate and unfiltered material. Furthermore, the provision of the woven drainage material means that a high percentage of filter-active depth is lost.
U.S. Pat. No. 4,007,114 issued Feb. 8, 1977, in the name of Eugene Ostreicher, and entitled FIBROUS FILTER MEDIUM AND PROCESS, discloses the use of melamine-formaldehyde colloids to modify a negative charge on high surface area fibrous filter materials in order to enhance what is known as electrokinetic capture of fine particle suspended solids (to thus remove the solids from the medium being filtered). The nature of electrokinetic capture is discussed in the '114 patent, in cols. 1-5 thereof. Also discussed is the effect, in carrying out filtering in general, of "mechanical straining". The disclosure of this patent is hereby incorporated into the disclosure of the present application, by reference.
U.S. Pat. No. 4,007,113 discloses another type of charge-modified filter, and the disclosure of this patent is hereby also incorporated by reference, into the disclosure of the present application.
Specific charge modifiers such as polyamide-polyamine-ephychloro-hydrin-resins are described in U.S. Pat. Nos. 2,926,116; 2,926,154; 3,224,986; 3,332,901; and 3,382,096; the disclosures of each of the above patents are incorporated herein, by reference.